Tuner



Feb. 9, 1960 R. H. PETERSON TUNER Filed July 26, 1955 DIV.

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lso- LAToR OCTAVE [03 SELECTOR OSCILLATO R d NoTE SELECTOR INVENTORRICHARD H. Pn'EnsoN T0 NOTE SELECTOR United States Patent O TUNERRichard H. Peterson, Chicago, Ill. Application July 26, 19,55, SerialNo.A 524,500

4 Claims. (Cl. 324-79) My invention relates to tuning musicalinstruments, and to electronic equipment for doing so. More specically,it relates to an electronic tuning standard of great stability, and toconvenient electronic means for comparing the frequencies of thestandard and of the instrument being tuned.

In the accompanying drawings:

Figure l is a general wiring diagram, with certain of the partsidentified by block showing for convenience and simplicity;

Figure 2 is a wiring diagram of a frequency changer; and

Figure 3 is a wiring diagram of the oscillator and its isolationamplifier.

The musical scale, known as the equal tempered chromatic scale, is knownto be a compromise, because the ratios of the musical pitches are notexactly in the ratios of small integers. Thus, based on A3 435, C3 is258.65, but G3 is not 387.98. Instead, it is 387.54, and such fractionaldiscrepancies in frequency permeate the entire series of compromisesthat make it possible for a single instrument to play in different keys.

The adjustment of these discrepancies, in a musical instrument, makes adifference in performance that is very marked to the trained ear of aperson of aesthetic sensibilities; and many great musical artists areextremely exacting in requiring pianos, harps, etc., to have a certaintemperament, even to the extent of taking with them their own piano, ortheir own personal piano tuner, or both.

According to the invention it is possible to provide a referencestandard of such accuracy and precision that the standard itself can bemade up to give a particular desired temperament. The complete adjustedstandard, then, enables a person of mediocre, or even non-existent,discrimination by ear with respect to pitchto produce and reproducerepeatedly the temperament determined by the reference standard.

In the embodiment selected to illustrate the invention, the oscillator lis of exceptional characteristics, in the sense that the frequency itgenerates is completely independent of variations in power-line voltageand powerline frequency. It is also independent of the condition or ageof the tubes. It is provided with tuning means to cause it to generateat least one complete octave of notes, with the temperament constant anddependable.

The signal from the oscillator may be compared with the correspondingnote of the instrument to be tuned by ear, or. the signal from thestandard and from the instrument to be tuned can be combined,electronically or otherwise, to generate a beat parison will give onecomplete octave with the exact temperament desired.

Having retained one complete octave of perfect ,tem-

yperament, it is quite possible to go down or up the scale by ear andtune all the other octaves, but that requires a sensitive and trainedear, and is a relatively exacting task. According to the invention, aseries of frequency This simple comchangers is used so that the operatorcan switch over from the oscillator signal itself to the output of a rstfrequency divider or multiplier and tune the adjacent octave, and so ondown or up as far as desired. In the embodiment illustrated, only sixoctaves are provided.

The basic temperament vThe oscillator 10 conveniently includes a tappedinductance 12 for the purpose of tuning it with precision to each of thenotes of a complete octave. The working inductance comprises vtwoportions in every instance. There is the pre-selected fraction of themain inductance 12, and a series of relatively much smaller trimmercoils 14, 16, 18, 20, 22, 24,26, 28, 30, 32, 34, 36 and 38, associatedin series relationship with the taps on the main inductance.

In each instance, the magnitude of the operating portion of the maininductance 12 is many times greater than that of the trimmer coil. Themain inductance has little or no ferro-magnetic action; in the bestdesigns, none at all. Therefore, its inductance is substantiallyindependent of circuit constants and voltages. A minor fraction, usuallyamounting to less than one percent, of the total inductance iscontributed by the trimmer coil, which can be adjusted by a simpleferro-magnetic core 40 over a narrow range. It will be obvious that ifthe actual magnitude of the trimmer coil inductance is one percent ofthe total, a variation of one percent in the trimmer coil will onlyrepresent a variation of one one-hundredth of one percent in the totalinductance. In vthis way a very quick and precise adjustment fortemperament can be provided, which will remain for long periods of timeso unaffected by any operating condition that the most sensitive eardoes not detect the variation.

The frequency delivered by the oscillator is a function of both theinductance and the capacitance of the tuned circuit. I have illustrateda primary capacitor 42 especially constructed to remain of constantcapacity over long periods of time and wide variations of temperature.To provide capacitors of such quality throughout the apparatus as awhole would be prohibitively expensive, but the cooperating relationshipbetween this capacitor and the others is such that the others can berelatively cheap and ordinary capacitors of a much lower degree ofconstancy without atfecting the eifective constancy of the tuner as awhole.

Thus, in parallel with capacitor 42 there is provided a series ofadditive capacitors, of which ten are illustrated. Any selected one ofthe trimming capacitors 44, 46, 48, 50, 52, 54, 56, 58, 60 and 62, maybe connected by the selector switch 64, in parallel with capacitor 42;land these capacitors are of progressively increasing size, such thatthe first one will lower the frequency about 0.05 of a semi-tone, andthe next will lower it 0.1 of a semi-tone, and so on. This degree ofprecision is essential to make it possible to tune one piano or pipeorgan etc., unto perfect unison with another instrument which hasalready been tuned. It will be apparent that all the trimming capacitorsmay be ordinary relatively cheap condensers not particularly immune toslight variations due to temperature or humidity. These trimmingcapacitors adjust the basic pitch of the entire reference standardwithout any change in its temperament.

Referring now to Figure 3, the oscillator 10 illustrated is a form of aHartley oscillator, but the grid capacitor 66 is exceptionally small,for instance, three percent of the capacitance of the main tuningcapacitor 42. I have found that careful adjustment of this ratio can bemade to produce an oscillator of highly constant frequency, regardlessof tube age, or the voltage supplied, or any other operating condition.

From the oscillator 10, the signal goes iirst to the isolator 68. Thisis an ordinary triode amplifier, except that it is operated as alimiter, and distorts the sine wave signal of the oscillator to acomplex wave form. In addition, its output voltage remains relativelyconstant even though the amplitude of the oscillation received may varysomewhat, depending on which semi-tone the oscillator 10 is delivering.

In a typical instance, this frequency band may cover the semi-toneswithin a range from about 2048 cycles per second to about 4096 cycles.The precise values may be Varied by the user, depending on the previousadjustment of the trimming capacitors.

The signal from the isolator 68 is delivered toy the grid of a secondtube at 70 forming part of `the first frequency changer 72. Thisfrequency changer is a divider, and one of several types well known inthe art,

and commonly referred to as anEccles-Jordan circuit. The triodes 74 and76 are interconnected in such a way that when either one is conducting,it will bias the other one and prevent the other one from conducting,but the trigger impulse from the tube 70 will upset this bias and letthe tube that was previously not conducting begin to conduct and preventits companion tube from continuing to conduct. Thus, each of the tubes74 and 76 functions in an on-and-oif or ip-ilop fashion, and the tubeschange places each time an impulse is received from the tube 70, so thatthe cycle of each of `these tubes requires two cycles of the tube 70 toarrive at completion.

From the divider 72 a conductor delivers signal to terminal of theoctave selector 78, and with the selector turned to that terminal, theuser may now tune the octave between the frequencies of 1024 and 2048 bymoving the note selector consecutively from one note to the next.

Fromthe divider 72 a; conductor `80 delivers'signal to the tube 70 ofthe second frequency divider 82. Therefore, the main tubes of the secondfrequency divider will complete their cycle during two cycles of thefirst frequency divider. From the second Vfrequency divider a conductor84 delivers the signal from that divider to terminal 4 of the octaveselector. I

- It will be apparent that any number offrequency dividers can beconnected in a cascade in this way, and that each frequency divider canhave'its resistors and capacitors proportioned to function efficientlyfor the frequencies which it receives and delivers. I have illustratedonly live dividers, in which the divider 82 takes care of the octavefrom 512 to 1024; the divider 86 covers from 256 to 512; the divider 88covers from 128 to 256; and the divider 90` from 64 to 128.

Beat com parison The signal from the octave selector may be delivered toa loud speaker through the capacitor 92, protective resistor 94 andpotentiometer resistor 96, Vfor Volume control by the user. The signalis amplified conventionally by tubes 98 and 100, and delivered to theprimary winding 102 of a conventional loud speaker 103.

A person with a fairly well-trained ear can do an excellent job bymerely listening to the instrument and to the reference loud speaker103. However, to speed up the work of such a person, and to enablepersons whose own musical discrimination'is insufficient to do equallygood work, means are provided for producing a beat note. The terminals104 may be yconnected to a microphone receiving the tone of theinstrument' being tuned. In the case of an electronic instrument, theterminals 104 may be connected directly to the appropriate terminals ofthe electronic instrument. The signal coming into the terminals 104 istransferred by a conventional transformer 106 and delivered at the point108 where it blends with the signal coming in from the octave selectorand produces a beat in the transformer 110.

The 15 ohm, 10 watt resistor 112 is a dummy load to replace the normalload on the electronic musical instrument. It yassures normalfunctioning of the instrument being tuned during the tuningvoperation.

The sharpness ofthe beat in the loud speaker 103 is materially enhancedif distortion is introduced into the amplifier circuit. I haveillustrated a distorting circuit comprising conductor 114, rectifier 116and conductor 118. 'I'he distorting circuit is rendered operative bycontacts 120 carried by the same conventional jack as terminals 104.

It will be noted that selection and installation of all trimmercapacitors is completed at the factory, and this part of the equipmentis never touched or disturbed by the user. which are carefully adjustedat the factory as one of the final stages of manufacture of the unit andare never adjusted by the user.

Others may readily adapt the invention for use under various conditionsof service by employing oner or more of the novelr features disclosed,or equivalents thereof.

For instance, the oscillator could operate one or more octaves lower orhigher, with a corresponding change in the number of frequency dividers,or with no frequency dividers at all. It could also be provided withfrequency multipliers to deliver any desired number of octaves abovethat are generated by the oscillator itself. A relatively smalladjustable capacitor 122 connected in parallel with capacitor 66 willchange the ratio or spread of the frequencies of the differentsemi-tones to get extra precision in frequency.

With respect to the apparent scope of my invention, I desirey to claimthe following subject matter:

1. In a high precision tuner, of the type comprising a precisionreference standard oscillator and means for comparing oscillations fromsaid standard with oscillations from the instrument being tuned; areference oscillator comprising a triode and a tank circuit; said tankcircuit comprising an inductor and a capacitor; said triode having acathode and a grid and a plate; said inductor having a `series ofsemi-tone taps corresponding to the twelve notes of the chromatic scale;a grid-cathode circuit including a selector switch, a connection fromsaid grid to said selector switch; said selector switch engaging aselected one of said semi-tone taps; said inductor having a cathode tapconnected to said cathode; a D.C. blocking capacitor inserted in saidgrid cathode circuit between said selector switch and said grid; saidblocking capacitor being of very small capacitance compared to said tankcircuit capacitor, and of the order of magnitude of three per cent ofsaid tank circuit capacitance.

2. A combination according to claim l in which said tank circuitinductor has said semi-tone taps positioned to secure the pitches of thenotes of the musical chromatic scale with approximate accuracy; therebeing a small adjustable trimming inductor in series with each of saidtaps for precision adjustment of each semi-tone; said tank circuitcapacitance including said first-mentioned capacitor, and a plurality ofsmaller trimming capacitors, arranged to be connected selectively inparallel with said main capacitor to adjust the overall frequency of allthe semitones without affecting the relative frequency ratios, ortemperament, determined by said main and tap inductors.

3. A combination according to claim 2, in which said trimmer inductorsare provided with ferromagnetic cores; said main inductor being devoidof magnetic material.

4. A combination according to claim 2, in which said inductor tapsinclude only twelve adjacent semitones; there being a cascade of 2-to-lfrequency dividers controlled by said reference standard; and additionalconnections for comparing the oscillations of the instrument being tunedwith the output signal from any selected one of said dividers.

(References ou following Page) The same applies to all the trimmercoils, l

5 References Cited in the le of this patent 2,730,681

UNITED STATES PATENTS 1,846,314 Crossley Feb. 23, 1932 1,947,187 ClarkFeb. 13, 1934 5 1,982,340 Forbes Nov. 27, 1934 2,087,652 Oakley July 20,1937 2,543,629 Hanert Feb. 27, 1951 2,680,198 Bick June 1, 1954 pgs.448-464.

6 Went Ian. 10, 1956 Krauss Sept. 17, 1957 Tennes Sept. 17, 1957 OTHERREFERENCES The Temperature Coecent of Inductance, article, Proceedingsof the I.R.E., April 1937, vol. 25, No. 4,

